In my third year gardening, I continue to evaluate what is worth growing and what isn't--for both financial and other reasons. Lettuce (all greens really), herbs, and tomatoes are all no-brainers, as they are easy and economical. So are berries, asparagus (worth the wait!), and rhubarb.
Another favorite of mine is beans. The last two summers I had a fair amount of success with lima beans, and this summer I added black eyed peas. Look how gorgeous the flowers are:
The great thing about beans is they don't need much fertilizer (they fix their own nitrogen). They also can be eaten/frozen fresh or dried.
I'm still on the fence about peppers, cucumbers, and squash, but it is fun learning in the process.